netdev - Re: [PATCH RFC 1/2] net: macb: Check DMA mappings for error

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Date:	Sun, 23 Feb 2014 00:13:13 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Soren Brinkmann <soren.brinkmann@...inx.com>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Michal Simek <michal.simek@...inx.com>
Subject: Re: [PATCH RFC 1/2] net: macb: Check DMA mappings for error

On Fri, 2014-02-21 at 11:30 -0800, Soren Brinkmann wrote:
[...]
> --- a/drivers/net/ethernet/cadence/macb.c
> +++ b/drivers/net/ethernet/cadence/macb.c
> @@ -632,11 +632,16 @@ static void gem_rx_refill(struct macb *bp)
>  					   "Unable to allocate sk_buff\n");
>  				break;
>  			}
> -			bp->rx_skbuff[entry] = skb;
>  
>  			/* now fill corresponding descriptor entry */
>  			paddr = dma_map_single(&bp->pdev->dev, skb->data,
>  					       bp->rx_buffer_size, DMA_FROM_DEVICE);
> +			if (dma_mapping_error(&bp->pdev->dev, paddr)) {
> +				dev_kfree_skb(skb);
> +				break;
> +			}
> +
> +			bp->rx_skbuff[entry] = skb;

This bit looks good.

>  			if (entry == RX_RING_SIZE - 1)
>  				paddr |= MACB_BIT(RX_WRAP);
> @@ -1040,6 +1045,10 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
>  	netdev_vdbg(bp->dev, "Allocated ring entry %u\n", entry);
>  	mapping = dma_map_single(&bp->pdev->dev, skb->data,
>  				 len, DMA_TO_DEVICE);
> +	if (dma_mapping_error(&bp->pdev->dev, mapping)) {
> +		dev_kfree_skb(skb);

You need to unlock bp->lock before returning.  Also, I think this should
be kfree_skb(), as that can be observed through dropwatch whereas
dev_kfree_skb() is completely silent.

Ben.

> +		return NETDEV_TX_OK;
> +	}
>  
>  	tx_skb = &bp->tx_skb[entry];
>  	tx_skb->skb = skb;

-- 
Ben Hutchings
All the simple programs have been written, and all the good names taken.

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